The present application is related to subject matter disclosed in Japanese Patent Application No. 2000-278526 filed on Sep. 13, 2000 in Japan to which the subject application claims priority under Paris Convention and which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a batch-type heat treatment apparatus for heat-treating in batch a number of objects-to-be-processed, such as semiconductor wafers or others, more specifically, to a batch-type heat treatment apparatus of adaptive control-type which estimates temperature of loaded semiconductor wafers and, based on an estimation result, conducts optimum control, and to a control method for the batch-type heat treatment apparatus.
2. Related Background Art
As batch-type heat treatment apparatus for performing film forming processing, oxidation processing or diffusion processing on a number of semiconductor wafers in batch, horizontal heat treatment apparatus and vertical heat treatment apparatus are known. Recently, the vertical heat treatment apparatus have become dominant for the reason that the vertical heat treatment apparatus take in little atmospheric air.
FIG. 1 is a view showing the appearance of the conventional heat treatment apparatus. This heat treatment apparatus comprises a vertical heating furnace 11, and a wafer boat 12 which is a wafer holder. The heating furnace 11 has heaters provided around a vertical reaction tube. A gas feed pipe 11a and an exhaust pipe 11b are connected to the heating furnace 11.
The wafer boat 12 has a plurality of support rods 13. Objects-to-be-processed, wafers W, have the peripheral edges supported in grooves formed in the respective support rods 13, whereby the wafers W are held, laid one above the other in shelves-like manner at a certain pitch. The wafer boat 12 with a number of wafers W mounted on is loaded into the heating furnace 11 through an opening formed in the bottom of the heating furnace 11 to be subjected to a required heat treatment.
In the control system of such heat treatment apparatus, treatment conditions (target values of treatment parameters), such as treatment temperature, treatment pressure, gas flow rate, etc., are determined corresponding to, e.g., a kind, a thickness, etc. of a thin film to be formed. A plurality of recipes containing these treatment conditions is prepared. Respective operators select recipes corresponding to kinds and film thicknesses of thin films to operate the heat treatment apparatus, based on the pre-determined treatment conditions.
The heat treatment apparatus makes heat treatments while controlling treatment conditions, such as treatment temperature, treatment pressure, gas flow rate, etc., to correspond to target values of the recipes.
For a suitable treatment, temperatures of the wafers, internal pressures of the heating furnace, gas flow rates, etc. must be measured.
Internal pressures in the heating furnace, and gas flow rates can be relatively correctly measured respectively by a pressure gauge and a mass flow controller or others, which includes a flow meter disposed in the feed pipe. However, it is difficult to measure wafer temperatures.
It can be proposed, for example, to mount temperature sensors on wafers and load the wafers in the heating furnace. However, no semiconductor element can be formed on portions where the temperature sensors are mounted on, and there is a risk that the interior of the heating furnace is generally polluted to resultantly lower yields of semiconductor devices.
It can be proposed to measure temperatures of an ambient atmosphere around the wafers. However, this method cannot correctly measure temperatures of the wafers.
Art for solving these problems is disclosed in, e.g., the specification of U.S. Pat. No. 5,517,594. In this art, a plurality of temperature sensors are arranged in a heating furnace, and temperatures of wafers are estimated second after second by using a mathematical model, based on outputs of the temperature sensors, electric powers fed to heaters, etc., so as to control electric powers of the heaters.
This art can incontiguously measure (estimate) wafer temperatures relatively correctly to thereby control a heat treatment apparatus without causing metal contamination.
However, even by this art, temperatures estimated (computed) based on the mathematical model do not often correspond to real temperatures due to, e.g., difference between a real system and a system used in preparing the mathematical model, and difference between environments for a real heat treatment and environments where the mathematical model was prepared, different processes, etc. In such cases, heater power is controlled, based on erroneous wafer temperatures, and required treatments cannot be made on wafers.
One object of the present invention is to provide a heat treatment apparatus which estimates temperatures of objects-to-be-processed by using a mathematical model to make heat treatments, based on the estimated temperatures of the objects-to-be-processed, and which can estimate correct temperatures of the objects-to-be-processed.
Another object of the present invention is to provide a batch-type heat treatment apparatus which can fabricate semiconductor devices of high reliability and high yields, and a method for controlling the batch-type heat treatment apparatus.
To achieve the above-described objects, the batch-type treatment apparatus according to the present invention comprises a heating furnace including a heater and a temperature sensor, for an object-to-be-processed to be loaded in; a first-temperature-estimator for estimating a temperature of the object-to-be-processed in the heating furnace, based on an output of the temperature sensor, by using a model for estimating a temperature of the object-to-be-processed in the heating furnace and a temperature of the temperature sensor itself, based on an output of the temperature sensor; a second-temperature-estimator for estimating a temperature of the temperature sensor itself by using the model; a corrector for correcting the temperature estimated by the first-temperature-estimator, based on the temperature indicated by the output of the temperature sensor and the temperature of the temperature sensor estimated by the second-temperature-estimator; and a controller for controlling the heater, based on a temperature corrected by the corrector.
According to this invention, temperatures of the temperature sensor are really metered and estimated by using the model. Relationships between the estimated temperatures and the really metered temperatures can be given. Temperatures of an object-to-be-processed and temperatures of the temperature sensor are estimated by the common model, which makes the relationships between the really metered temperatures and the estimated temperatures of the temperature sensor applicable substantially similarly to relationships between real temperatures and estimated temperatures of the object-to-be-processed. Such relationships, etc. are applied to the estimated temperatures of the object-to-be-processed, whereby the estimated temperatures of the object-to-be-processed are corrected to give substantially correct temperatures of the object-to-be-processed, and by using the correct temperatures of the object-to-be-processed, the heater can be controlled.
The corrector includes means for giving a relationship xe2x80x9cfxe2x80x9d between, for instance, the temperature estimated by the second-temperature-estimator and the temperature indicated by the output of the temperature sensor, and applying to the relationship xe2x80x9cfxe2x80x9d the temperature of the object-to-be-processed estimated by the first-temperature-estimator to thereby correct the temperature of the object-to-be-processed estimated by the first-temperature-estimator.
Specifically, the corrector gives, for instance, an offset (offset=really metered temperaturexe2x88x92estimated temperature) of the temperature indicated by the output of the temperature sensor from the temperature, as a reference, estimated by the second-temperature-estimator, and adds the offset to the temperature estimated by the first-temperature-estimator to thereby correct the temperature of the object-to-be-processed estimated by the first-temperature-estimator.
Otherwise, the corrector gives a ratio xe2x80x9ckxe2x80x9d (K=really metered temperature/estimated temperature) of the temperature indicated by the output of the temperature sensor to the temperature of the temperature sensor estimated by the second-temperature-estimator, and multiplies the temperature of the object-to-be-processed estimated by the first-temperature-estimator with the ratio xe2x80x9ckxe2x80x9d to thereby correct the estimated temperature of the object-to-be-processed.
The above-described model includes a heater control model for controlling the heater to approximate the estimated temperature of the object-to-be-processed to a target value.
The above-described model is for estimating a temperature, e.g. the temperature of the object-to-be-processed in the heating furnace and the temperature of the temperature sensor itself, based on a temperature, e.g. the output of the temperature sensor and a control signal for the heater. The first-temperature-estimator estimates the temperature of the object-to-be-processed in the heating furnace, based on the output of the temperature sensor and the control signal for the heater, and
the second-temperature-estimator estimates the temperature of the temperature sensor, based on the output of the temperature sensor and the control signal for the heater.
The above-described controller includes a recipe memory for storing a recipe for temperature changes to be applied to the object-to-be-processed, and the controller controls the temperature estimated by using the model so that the estimated temperature of the object-to-be-processed changes in accordance with the recipe stored in the recipe memory.
The above-described recipe memory stores recipes corrected corresponding to a plurality of zones of the interior of the heating furnace divided in the direction of arrangement of the objects-to-be-processes, and the controller controls the heaters in accordance with the recipes for the respective zones.
The above-described controller controls the heaters so that offsets of sets of the estimated temperatures of the objects-to-be-processed corrected by the corrector from sets of temperatures indicated by the recipes for the plural zones are minimized.
To achieve the above-described objects, the method for controlling a batch-type heat treatment apparatus according to the present invention comprises a heating furnace including a heater and a temperature sensor, for an object-to-be-processed to be loaded in, comprises estimating a temperature of an object-to-be-processed in the heating furnace and a temperature of the temperature sensor itself, based on an output of the temperature sensor by using a model for estimating a temperature of the object-to-be-processed in the heating furnace and a temperature of the temperature sensor itself, based on an output of the temperature sensor; comparing a temperature indicated by the output of the temperature sensor with the temperature of the temperature sensor estimated by using the model; correcting the estimated temperature of the object-to-be-processed in accordance with a comparison result; and controlling the heater in accordance with a corrected temperature of the estimated temperature of the object-to-be-processed.